Couple of months ago, Microsoft published the Visual Studio 2010 CTP version at this link. The files total size was a whopping 7GB. when extracted it took another ~24GB of space. the reason is that it contains a full Virtual pc environment running Windows server 2008 and VS2010 already installed.
The problem was that on the first of January 2009 the version had expired and couldn't be used any more. Jeff Beehler posted a temporary solution in his blog on how to override this problem in case you need more time to evaluate it. Remember, do the change before you open the VS2010.
BTW, this will also solve the nagging windows activation message.